No, I would say it makes sense to keep those under the Xbox 360 platform. However, in the "Game Info" section, I was thinking of adding some category tags that users could filter games by. So I might add a tag for backwards compatibility there.

Yes, we only show the challenges. Uplay achievements aren't shown on the site currently. Ubisoft has made those fully private, they are visible only in the Uplay client and others can't see them even if they are on your friends list. If/when they change that, then I'll add support.